This application is based upon Japanese Patent Application No. 2000-252419 filed on Aug. 23, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus for controlling a motor-driven cooling fan for a vehicle.
2. Related Art
A vehicle (for example, automobile) is provided with a cooling fan for cooling a radiator of an engine, a condenser of an air conditioner, and the like. Conventionally, the cooling fan is driven by a DC motor (with a brush). By using the cooling system, different from the configuration of coupling the cooling fan to the output shaft of the engine and rotating the fan by the engine, the cooling fan can be driven and stopped directly by the motor, and its rotational speed can be set independent of the rotating state of the engine.
However, since the motor for rotating the cooling fan is driven on the power supplied from a battery, as compared with the case where the cooling fan is driven by the engine, the balance between charging and discharging of the battery, that is, the balance between generated power and consumed power in a vehicle deteriorates. In recent years, therefore, a technique of using a brushless motor having higher motor efficiency in place of a DC motor (with a brush) has been proposed. In this case as well, it is difficult to largely reduce the power consumed to rotate the cooling fan.
The invention has been achieved in consideration of the circumstances and its object is to provide an apparatus for controlling a motor-driven cooling fan for a vehicle, capable of achieving an improved power balance.
According to first aspect of the invention, when a vehicle travels, a flowing air passes through a cooling fan for vehicle, and the cooling fan for vehicle is rotated by the traveled flowing air. Thus, a motor works as a regenerative apparatus which generates energy in association with the rotation of the cooling fan (motor). As a result, a battery is regenerated in electric power. Consequently, even when the cooling fan for vehicle is driven by a motor, a relationship between consumed power and generated power (hereinafter, power balance) in the vehicle can be improved. Particularly, in the case of a vehicle, different from a device receiving natural wind, as the vehicle travels, the flowing air passes through the vehicle at relatively high speed. Consequently, the rotating energy of the cooling fan for vehicle by the flowing air is large, and the large regenerative energy can be therefore obtained. Therefore, the power is prevented from being consumed largely.
When the rotational speed detected by the rotational speed detecting means is equal to or higher than a predetermined value, the regenerative apparatus regenerates the energy by the motor. Consequently, only when a regenerative energy of a certain quantity is expected, that is, only when the power balance in the vehicle is effectively improved, the regenerating operation can be executed.
According to the invention, the regenerative apparatus stores (charges) the energy which is generated by the motor into power storing means (such as the battery). Even in the case where the generated energy to be regenerated changes every moment according to a change in the driving state of the vehicle such as a vehicle speed, regenerated energy can be effectively used. Since the regenerative apparatus stores (charges) the energy in a situation that the power storing means is not in a fully stored state, occurrence of an excessively stored state in the power storing means can be prevented.
According to the invention, in a case where the cooling fan for vehicle is rotated by a flowing air as the vehicle travels, a driving apparatus generates energy by using the motor in association with the rotation of the fan (motor). Even in the configuration of driving the cooling fan for vehicle by a motor, the electric power balance of the energy storing means in the vehicle can be improved. Further, since the driving apparatus for driving the motor has a function of generating energy so as to regenerate the energy of the energy storing means such as a battery, the configuration is simpler as compared with a configuration of separately providing the regenerative apparatus.
According to other aspect of the invention, a brushless motor having relatively high motor efficiency is used as the motor for rotating the cooling fan for vehicle. Thus, further improved power balance in the vehicle can be obtained.
According to other aspect of the invention, when an instruction of driving the cooling fan for vehicle is input, a control circuit outputs a drive signal for driving a brushless motor to a switching device constituting an inverter circuit. Moreover, the control circuit outputs a regenerative drive signal for regenerating the energy by the brushless motor when the drive signal is not output.
According to other aspect of the invention, the control circuit supplies an off signal to a switching device constituting an upper arm of an inverter circuit having a bridge circuit configuration, and supplies a switching signal having a predetermined frequency and a predetermined duty ratio to a switching device constituting a lower arm. With the configuration, voltage boosting operation and regenerating operation are simultaneously executed.
Specifically, when the lower arm switching device is turned on, a current flows in a stator winding via the lower arm switching device by an inductive voltage of the brushless motor. When the lower arm switching device is turned off, the current is returned to the input side of the inverter circuit via a flywheel diode disposed on the upper arm side. According to the means, even when the rotational speed, that is, the inductive voltage of the brushless motor is low, the inductive voltage can be regenerated while being boosted.
Other features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings.